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Thursday, July 14, 2011

Natural Shields Against Climate Change Weaker Than Anticipated

Former U.S. Vice President Al Gore plans to hit the climate crisishard with a day of organized global action on Sept. 14. Goreannounced his “Climate Reality Project”in this video. The dayof action aims to use 24 speakers to broadcast 24 straight hoursof climate activism, encouraging others to get up and undertakeclimate mitigation efforts as well.

The soil and the ocean are being weakened as buffers against global warming, in a vicious circle with long-term implications for the climate system, say two new investigations.

If the seas and the land are less able to soak up or store greenhouse gases, more of these carbon emissions will enter the atmosphere, holding in even more heat from the sun.

A study published in Nature [and ScienceDaily] says a gradual increase in atmospheric carbon dioxide (CO2) over the last half-century has accelerated the release of methane and nitrous oxide in the soil.

These gases are respectively 25 and 300 times more effective at trapping radiation than CO2, the principal greenhouse gas by volume.

"This feedback to our changing atmosphere means that nature is not as efficient in slowing global warming as we previously thought," said Kees Jan van Groenigen, a professor at Trinity College Dublin and the paper's lead author.

More carbon dioxide in the atmosphere causes soil to release the potent greenhouse gases methane and nitrous oxide, new research published in this week's edition of Nature reveals. "This feedback to our changing atmosphere means that nature is not as efficient in slowing global warming as we previously thought," said Dr Kees Jan van Groenigen, Research Fellow at the Botany department at the School of Natural Sciences, Trinity College Dublin, and lead author of the study.

Earlier studies examining how additional CO2 affects the capacity of different soils -- in forests, grasslands, wetlands and agricultural fields -- to either absorb or release these two gases yielded conflicting results.

Van Groenigen, along with colleagues from Northern Arizona University and the University of Florida, gathered all published research to date from 49 different experiments mostly from North America, Europe and Asia, and conducted in forests, grasslands, wetlands, and agricultural fields, including rice paddies. The common theme in the experiments was that they all measured how extra carbon dioxide in the atmosphere affects how soils take up or release the gases methane and nitrous oxide.W hen van Groenigen and colleagues reviewed the 49 studies two patterns emerged:

More CO2 increased nitrous oxide in all soils, but soils in rice paddies and wetlands released more methane in particular.

The culprits in both cases are microscopic soil organisms that breathe in CO2 and "exhale" methane. The more carbon dioxide in the air, the more these single-cell greenhouse-gas factories thrive.

The culprits are specialized microscopic organisms in soil, that respire the chemicals nitrate and carbon dioxide, like humans respire oxygen. The microbes also produce methane, a greenhouse gas 25 times more powerful than carbon dioxide, and nitrous oxide, 300 times more potent than carbon dioxide. Their oxygen-free habit is one of the reasons these microorganisms flourish when atmospheric carbon dioxide concentrations increase. Van Groenigen explained: "The higher CO2 concentrations reduce plant water use, making soils wetter, in turn reducing the availability of oxygen in soil, favoring these microorganisms."

The other reason these microorganisms become more active is that increasing CO2 makes plants grow faster, and the extra plant growth supplies soil microorganisms with extra energy, pumping up their metabolism. This extra plant growth is one of the main ways ecosystems could slow climate change. With more CO2, plants grow more, soaking up carbon dioxide through photosynthesis, and, the hope is that they also lock away carbon in wood and soil. But this new work shows that at least some of that extra carbon also provides fuel to microorganisms whose byproducts, nitrous oxide and methane, end up in the atmosphere and counteract the cooling effects of more plant growth.

"It's an ecological point and counterpoint: the more the plants soak up CO2, the more microbes release these more potent greenhouse gases," said Bruce Hungate, Professor at Northern Arizona University and co-author on the study. "The microbial counterpoint is only partial," continued Hungate, "reducing the cooling effect of plants by about 20%."

But it's an ecological surprise, too, and one that climate models will need to reckon with as they further refine pictures of the climate of the future. "By overlooking the key role of these two greenhouse gases, previous studies may have overestimated the potential of ecosystems to mitigate the greenhouse effect," says van Groenigen.

If the calculations are right, the carbon "credit" that is attributed to faster plant growth driven by extra CO2 in the air must be revised. This "credit" helps to offset the negative impact of greenhouse gases -- but the new data suggests it should be written down by a fifth.

The world's seas take up roughly one-third of all human carbon emissions, but how this "sponge" responds to rising CO2 levels is a tough question, mainly because data has been spotty geographically and didn't cover long time periods.

Galen McKinley, a professor at the University of Wisconsin at Madison, worked with a team that looked at three decades of observational data from the North Atlantic.

They found that rising air and water temperatures were slowing the pace at which carbon is absorbed across a large portion of this ocean's subtropical zones.

Up to now, scientists reasoned that only when carbon content in the ocean rose faster than in the atmosphere could one say that the capacity to take in CO2 had diminished. But the new study shows that the ocean "sink" can be weakened even without this visible sign.

"The ocean is taking up less carbon because of the warming caused by the carbon in the atmosphere... More likely, what we are going to see is that the ocean will keep its equilibration [the balance between atmospheric and ocean carbon levels] but it doesn't have to take up as much carbon to do it because it's getting warmer at the same time." Warmer water cannot hold as much CO2 as colder water, so as a result, as the ocean's temperature rises, its "carbon capacity" decreases, explains McKinley.

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